Radiation shielded electron discharge device

ABSTRACT

An electron discharge device is provided with shields to protect against inadvertent emission of penetrating electromagnetic radiation. The positions and mounting of the shields is designed to provide shielding in all directions which is relatively undefeatable by inadvertent tampering by the user.

United States Patent 1 1 Cullen et a1.

11] 3,736,457 1 May 29, 1973 RADIATION SHIELDED ELECTRON DISCHARGEDEVICE Inventors: William F. Cullen, Philpot, Ky.; Fred F. Holub,Schenectady, NY. Michael R. McCormick, Louisville; Ky.

General Electric Co., Owehsboro, Ky.

Filed: Mar. 25, 1971 Appl. No.: 128,056

Assignee:

11.8. CI ..3l3l3l3, 313/240 Int. Cl ..II0lj l/52, H0lj 19/40 Field ofSearch ..313/240, 313

References Cited UNITED STATES PATENTS 11/1960 Downing et a1. ..313/3132/1941 Atlee et al. ..3l3/313 X 3,534,215 10/1970 Hughes et al ..313/3133,603,716 9/1971 Koren ..3l3/3l3 X FOREIGN PATENTS OR APPLICATIONS573,660 11/1945 Great Britain ..3l3/313 Primary Examiner-David SchonbergAssistant Examiner-Toby H. Kusmer Attorney-Nathan J'. Cornfeld, John P.Taylor, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. FormanABSTRACT 9 Claims, 5 Drawing Figures Patented May 29, 1973 3,736,457

2 Sheets-Sheet 1 FIG.2.

INVENTORS: WILLIAM F. CULLEN, FRED F. HOLUB MICHAEL R. MCORMI THEIR ATTONEY.

Patented May 29, 1973 3,136,457

2 Sheets-Sheet 2 fines.

INVENTORS;

WILLIAM F. CULLEN,

FRED F. HOLUB, MICHAEL R. MCCORMICK,

BY MK:

THEIR ATTOR Y.

diation in industrial equipment BACKGROUND OF THE INVENTION Thisinvention relates to electron discharge devices. More particularly,thisinvention relates to means for mitigating the emission ofundesirable electromagnetic radiation from electrondischarge devices.

Electron discharge device used in high voltage applications such ashigh-voltage rectifiers have been known to emit undesirable levels ofpenetrating electromagnetic radiation particularly when a failure modeinthe high voltage system, for example, in a television receiver, causethe high voltage in the device to rise above normal operating levels.The increased use of such rectifiers at highervoltages in colortelevision has increased the need for protection against such radiation.

The usual approach to shielding from undesirable rais to employ a heavymetal such as lead. However, in a television receiver, theweightrequirements forbid the use of a large lead cage while insulationrequirements prevent the use of metal such as lead in intimate contactwith the walls of the tube. Furthermore, the shielding means must not bedefeatable by the removal and reinsertion of the tube in the chassis bythe user or other unskilled personnel.

The use of a non-metallic material as a jacket or shield for the tube isthus necessary. Unfortunately, however, most non-metallic materials donot, in general, provide sufficient radiation shielding, andfurthermore, are, particularly in the case of organic materials, subjectto degradation upon prolonged exposure to radiation. The use of certainfillers in, for example, plastic binders to increase the radiationshielding effect of the material has been suggested in the art such asUS. Pat. No. 3,114,721 assigned to the assignee of this invention.Furthermore, in an article published by E.I. DuPont deNemours andCompany entitled Hypalon Report No. 9, it is stated on page 10 thatHypalon 45, a chlorosulfonated polyethylene, is an excellent binder forradiation shielding and a subsequent table shows the high level ofloading with litharge possible.

However, due to the degradation mentioned above, the use of such fillersis complicated by thereduction of plasticity resulting from the use ofsufficiently high levels of such fillers to provide the desired amountof shielding coupled with the further increase in brittleness due to theradiation exposure. As an additional complicating factor, the additionof fillers having known radiation shielding properties can increase theflammability of a material.

SUMMARY It is therefore an object of the invention to provide a highvoltage electron discharge device having radiation attenuation meansintimately associated therewith which do not materially affect theelectrical insulation properties of the device.

It is a further object of the invention to provide radiation inhibitingmeans for an electron discharge device having low flammabilitycharacteristics and high resistance to both thermaland radiationdegradation.

These and other objects of the invention will be apparent from thespecification and accompanying drawmgs.

In accordance with the invention a high voltage discharge devicecomprising an evacuated cylindrical glass envelope having a plurality ofelectrodes therein is surrounded by radiation shielding means includingfirst shield means bonded thereto comprising elastomeric polymer meansincluding a radiation attenuating filler and a sufficient amount ofadditional filler to impart flame resistance to the shielding means.Auxiliary shield means are also provided to shield against radiationemanating axially from the device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectionalview of the invention.

FIG. 2 is an exploded view of a portion of FIG. 1.

F IG. 3 is a partially broken-away exploded view of an alternateembodiment of the invention.

FIG. 4 is a fragmentary, cross-sectional view of another embodiment ofthe invention.

FIG. 5 is a fragmentary, exploded view of another embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, anelectron discharge device constructed in accordance with the inventionis generally indicated at 2. The illustrated device is a high voltagerectifier comprising an evacuated cylindrical glass envelope 10 having aphenolic base 20 with a plurality of pins 22circularly mounted therein.Device 2 also contains an anode 40 and a cathode 30 which, in theillustrated embodiment, is an indirectly heated cathode. Anode 40communicates with the exterior of envelope 10 via an anode cap 42 whichpasses through envelope l0 and to which envelope 10 is sealed. Cathode30 is electrically attached to the appropriate pins 22 via leads 24which pass through envelope 10.

In accordancewith the invention, a first radiation shield 50 surroundsglass envelope 10. Radiation shield 50, which will be described in moredetail below, comprises a filled elastomeric material which ispreferably bonded to envelope 10 so that it cannot be removed by theuser.

Second and third radiation shields 60 and are mounted respectivelyadjacent the bottom and top of device 2 as viewed in FIGS. 1 and 2.Radiation shields 60 and 70 provide auxiliary shielding along the axisof device 2 to provide, in conjunction with the primary shield 50, acomplete shield which will intercept internally generated radiationregardless of direction.

In a preferred embodiment, shields 60 and 70 comprise metal discs ofnickel-plated steel of sufficient thickness to provide the desiredshielding. It has been found that an effective thickness of about milsprovides satisfactory shielding. Effective thickness is defined as theactual thickness of the shield (when nickelplated steel is used) plusthe additional thickness of the metal parts to which it is assembled aswill be more fully described below with respect to upper shield 70.

Other metals such as, for example, molybdenum or tungsten can be used.The particular thickness needed to provide an effective thicknesscomparable to the 80 mil thickness when nickel-plated steel is used willvary somewhat depending upon the density of the material. In any eventthe metal chosen must be consistent with good electron discharge devicematerial selection such as is well known to those skilled in the art.

Disc-like shield 60 is mounted within envelope preferably immediatelyabove the glass fillets 12 surrounding leads 24. Shield 60 is mountedgenerally coaxially with device 2 with the planes of the disc generallynormal to the axis of device 2. Shield 60 may be retained in thisposition by welding to appropriate leads 24.

Shield 70, in the preferred embodiment illustrated in FIGS. 1 and 2,comprises a disc of about 60 mils thickness. Disc 70 is assembledbetween anode 40 and anode cap 42 as best seen in FIG. '2. Thecylindrical sidewall 46 of anode 40 extends beyond end wall 44 to definea recess into which disc-like shield 70 is inserted. Anode cap 42 isthen placed on top of shield 70 within the recess and rim 48 of anodecap 42 is welded to shield 70 and end wall 44. The end of sidewall 46 isthen crimped over rim 48 at 49 as best seen in FIG. 1.

The effective thickness of radiation shield 70 is then the actualthickness of disc 70 plus the thickness of end wall 44 and the thicknessof either rim 48 or end wall 41 of anode cap 42. In the illustratedembodiment disc 70 is about 60 mils thick; end wall 44 is about 10 milsthick; and rim 48 and end wall 41 are each about 10 mils thick to give atotal effective thickness of about 80 mils.

Shields 60 and 70 are thus positioned within device 2 to act inconjunction with shield 50 to provide a complete three dimensionalradiation shield about the internal, active elements of device 2. Theadditional shields are necessary to provide complete surroundment of thedevice which cannot be done with a unitary shield unless a cage oflarger dimensions was used since some parts of the device must beaccessible for external electric connections. Complete shielding of thedevice is believed necessary because the source and direction of theradiations are not completely known and, even if the direction of thesource could be pinpointed, the scattering of the rays would stillnecessitate complete surrounding of the device to insure minimizing ofthe escape of any radiation. It should be understood, however, that theadditional shields need not be mounted within the device although thisis preferable from a standpoint of compactness.

Shield 50, as previously mentioned, is a filled elastomeric materialbonded to glass envelope 10. The use of a filler is basically necessaryto provide opaqueness to the radiation since organic materials arerelatively transparent to electromagnetic radiation. The preferredfiller material is lead oxide, other materials may be used, however,provided they possess the required radiation shielding properties and donot deleteriously effect the physical properties of the shield.

Shield 50, as best seen in FIG. 1, is generally cylindrical having aninner diameter generally conforming to the outer diameter of cylindricalenvelope 10. Shield 50 extends downwardly, beyond the terminus ofenvelope 10, to the bottom of phenolic base 20. Phenolic base 20 isconstructed of a slightly larger diameter than envelope 10 to provide aslight interference fit with shield 50 as well as to provide a surfaceto which shield 50 may be bonded. It should be noted here that base 20has been described herein as phenolic but may be constructed of otherinsulative materials as well. In fact, it is within the scope of thisinvention to construct base 20 of a material which, either with orwithout fillers, will have radiation attenuation properties equivalentto shield 50 thus eliminating the need for shield 60.

The elastomeric binder material must be sufficiently ductile anddeformable after compounding and forming into a sleeve to slip over theglass envelope. The binder material also must be sufficiently flameretardant to pass standardized tests for flame retardancy. The lattercharacteristic may be obtainable through the use, for example, of highlyhalogenated rubber compounds, blends of such compounds, with the aid offillers or additives having fire retardant properties, or combinationsof rubber compounds having flame retardant characteristics with flameretardant fillers or additives.

The binder material (as well as any fillers or additives) must also besufficiently radiation resistant to withstand the amounts of radiationto which the shield may be exposed over the life of the tube. The bindermust also be able to withstand prolonged exposure to heat without undueembrittlement.

Examples of elastomeric compounds which have been found to possess theabove properties and thus are useful as binder materials include, forexample, chlorinated polyethylene, chlorosulfonated polyethylene, andsilicone rubber.

The elastomeric binder material may be further defined as a materialhaving a glass transition temperature below zero centigrade; having alow initial viscosity to aid in the initial blending of the fillers intothe binder; and curable to a higher viscosity wherein the material isstill sufficiently ductile and deformable to permit mounting of a sleeveformed of the material onto the glass envelope of the electron dischargedevice.

As previously stated, the preferred filler material to impart thedesired radiation shielding is lead oxide. Preferably, the amount oflead oxide used is about 2.5-3.0 parts by weight lead oxide per partbinder. It has been found that this ratio provides sufficient binder toimpart the desired ductile properties and sufficient lead oxide toprovide a factor of about ten radiation attenuation per about 0040-0045inch thickness. Other filler materials can be substituted for the leadoxide if they provide this amount of shielding without the use of suchlarge amounts of filler as to impair the physical properties of thefinal product. In accordance with the invention a shield having a totalthickness of about 0.125 inch and constructed of materials providing aradiation attenuation factor of about 10 per 0.040-0.045 inch thicknesshas been found to be sufficient to lower the radiation levels to below0.1 milliroentgens per hour.

As previously stated, a fire-retardant filler material or additive maybe used, if necessary, to impart further flame retardancy to thematerial. In accordance with the invention the final material mustpossess, in addition to the required radiation shielding and physicalproperties, sufficient flame retardancy with or without additional flameretardant additives to pass the SE-l test of the fire underwriterslaboratories.

In accordance with a preferred embodiment of the invention, and as aspecific illustration thereof, parts by weight of a chlorosulfonatedpolyethylene elastomer containing about 25-30 percent by weight chlorineand about l1.5 percent by weight sulfonyl chloride was blended with 275parts by weight of PhD; 100 parts by weigh of A1 0 31-1 0; and about 25parts by weight of chlorinated paraffin plasticizer. One part by weightTetrone A (dipenta methylene-thiuramtetrasulfide) and 0.5 parts byweight MBTS (benzothiazyl disulfide) were added as curing accelerators,no additional catalyst being necessary in the particular system due tothe presence of PbO which acts as a curing agent for chlorosulfonatedpolyethylene. About 20 parts by weight of Thermax, a carbon blackpigment, was added to impart a grey color to the material.

The material was molded into a 0.125 inch thick shield and bonded to theglass envelope of an electron discharge device using a rubber contactcement. The electron discharge device was internally fitted with theaxially mounted metal shields previously described. The device wasoperated at 42KV and radiation measurements taken to test theeffectiveness of the primary shield. No emissions over 0.1milliroentgens per hour (the limit of the sensitivity of the equipment)were measured.

Referring now to FIGS. 3-5 alternate embodiments are illustrated whichrelocate the secondary shields to positions outside envelope 10. In FIG.3, shield 60 has been replaced by a disc 160 which may be constructed ofthe same material as primary shield 50. Disc 160, when constructed ofthe same material as shield 50, has a comparable thickness, e.g. about0.125 inch and is provided with tiny holes 162 through which leads 24may pass. Disc 160 is constructed of approximately the same diameter asbase 20 on which it is seated. Leads 24 pass through holes 162 and areattached in conventional manner to pins 22 on base 20. Disc 160 may bemolded with a central depression defining a concave central portion onthe upper surface and a convex central portion on the lower surface toaccommodate the exhaust tip of glass envelope without changing theoverall shield thickness.

In FIG. 4 a construction is illustrated which is capable of replacingshield 70. In the illustrated embodiment, the top cap metal connectorcup 174 and lead 176 are embedded in a molded insulated shield 170 whichis constructed of the same material as shield 50 and to a comparablethickness. While FIG. 4 shows the shield lead as demountable, it may beintegrally formed with shield 50 as a one piece assembly. The latterconstruction actually is preferred since the shielding cannot, then, bedefeated by the user of the device. In FIG. 5, another construction isillustrated in which a metallic cap or thimble 270 is placed over anodecap 42. Thimble 270 is constructed of sufficient thickness to provide aneffective total thickness of 80 mils as previously discussed. Thimble270 is preferably non-detachably mounted to anode cap 42 after shield 50has been installed. A conventional connector cup 274 properly sized tothe outer diameter of thimble 270 is illustrated as providing externalelectrical contact to the anode Thus, the invention provides an electrondischarge device which is completely shielded to eliminate the emanationof harmful amounts of electromagnetic radiation. The device is lightenough to be removable from a television chassis yet durable towithstand prolonged exposure to both heat and radiation. The device isrelatively fireproof and its radiation shielding properties arerelatively undefeatable by inadvertent tampering by the user as mighthappen with removable shielding.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A high voltage electron discharge device comprising an evacuatedcylindrical glass envelope having a plurality of electrodes therein andbeing surrounded by radiation shielding means intimately associated withsaid device comprising: first shield means bonded to said envelopecomprising elastomeric polymer binder means including a radiationattenuating filler in an amount sufficient to provide a radiationattenuating factor of about 10 per 0.040-0.045 inch thickness of saidfirst shield, and having flame retardant means therein; and secondshielding means adjacent said envelope comprising a plurality of shieldmeans coaxially mounted generally normal to the axis of said deviceincluding at least one shield mounted adjacent one end of saidcylindrical envelope and at least one other shield mounted adjacent theopposite end of said envelope, said shields cooperating to provide acomplete shield which will intercept internally generated radiationregardless of direction.

2. The device of claim 1 wherein said filler is lead oxide and theamount of filler in said first shield is about 2.5-3 parts by weight perpart binder.

3. The device of claim 1 wherein said second shielding means comprisemetallic discs mounted within said envelope and having an effectivethickness of about mils and sufiicient diameter to provide, with saidfirst shield, complete surroundment of said electrodes.

4. The device of claim 1 wherein said second shielding means includes atleast one shield mounted externally of said envelope.

5. The device of claim 1 wherein one of said electrodes comprises ananode having an anode cap protruding from one end of said envelope and aseries of leads protruding from an opposite end of said envelope andsaid second shielding means includes a shield for said anode cap andanother shield in intimate contact with said leads protruding from saidenvelope, said shields being made of insulative material havingradiation-attenuating properties similar to said first shield and beingpositioned contiguous to said first shield.

6. The device of claim 1 wherein said binder is selected from the classconsisting of chlorinated polyethylene, chlorosulfonated polyethylene,and silicone rubher.

7. The device of claim 1 wherein said binder is chlorosulfonatedpolyethylene and said filler is lead oxide.

8. A high voltage electron discharge device comprising an evacuatedcylindrical glass envelope having a cathode and an anode therein andbeing substantially surrounded by a first shielding means comprising alead-oxide-filled chlorosulfonated polyethylene shield havingfire-retardant means therein and having a loading ratio of about 2.5 to3 parts by weight lead oxide per part binder and having a totalthickness of about 0.125 inches; said device having second shieldingmeans within said envelope comprising a first metallic disc having aneffective thickness of about 80 mils coaxially positioned in saidenvelope adjacent one end of said cylinder and a second metallic dischaving an effective thickness of about 80 mils positioned adjacent theopposite end of said cylinder, said discs being mounted normal to theaxis of said device and. having sufficient diameter to intersect anyradiation having a direction which would avoid intersection with saidfirst shield.

9. The device of claim 8 wherein said anode is connected to an anode cappassing through one end of said cylindrical glass envelope and saidcathode is connected to leads which pass through the opposite end ofsaid envelope and into a base comprising an insulating ter approximatelyequal to the diameter of said envelope to provide a snug fit thereon andan interference fit with said base.

1. A high voltage electron discharge device comprising an evacuatedcylindrical glass envelope having a plurality of electrodes therein andbeing surrounded by radiation shielding means intimately associated withsaid device comprising: first shield means bonded to said envelopecomprising elastomeric polymer binder means including a radiationattenuating filler in an amount sufficient to provide a radiationattenuating factor of about 10 per 0.040-0.045 inch thickness of saidfirst shield, and having flame retardant means therein; and secondshielding means adjacent said envelope comprising a plurality of shieldmeans coaxially mounted generally normal to the axis of said deviceincluding at least one shield mounted adjacent one end of saidcylindrical envelope and at least one other shield mounted adjacent theopposite end of said envelope, said shields cooperating to provide acomplete shield which will intercept internally generated radiationregardless of direction.
 2. The device of claim 1 wherein said filler islead oxide and the amount of filler in said first shield is about 2.5-3parts by weight per part binder.
 3. The device of claim 1 wherein saidsecond shielding means comprise metallic discs mounted within saidenvelope and having an effective thickness of about 80 mils andsufficient diameter to provide, with said first shield, completesurroundment of said electrodes.
 4. The device of claim 1 wherein saidsecond shielding means includes at least one shield mounted externallyof said envelope.
 5. The device of claim 1 wherein one of saidelectrodes comprises an anode having an anode cap protruding from oneend of said envelope and a series of leads protruding from an oppositeend of said envelope and said second shielding means includes a shieldfor said anode cap and another shield in intimate contact with saidleads protruding from said envelope, said shieldS being made ofinsulative material having radiation-attenuating properties similar tosaid first shield and being positioned contiguous to said first shield.6. The device of claim 1 wherein said binder is selected from the classconsisting of chlorinated polyethylene, chlorosulfonated polyethylene,and silicone rubber.
 7. The device of claim 1 wherein said binder ischlorosulfonated polyethylene and said filler is lead oxide.
 8. A highvoltage electron discharge device comprising an evacuated cylindricalglass envelope having a cathode and an anode therein and beingsubstantially surrounded by a first shielding means comprising alead-oxide-filled chlorosulfonated polyethylene shield havingfire-retardant means therein and having a loading ratio of about 2.5 to3 parts by weight lead oxide per part binder and having a totalthickness of about 0.125 inch; said device having second shielding meanswithin said envelope comprising a first metallic disc having aneffective thickness of about 80 mils coaxially positioned in saidenvelope adjacent one end of said cylinder and a second metallic dischaving an effective thickness of about 80 mils positioned adjacent theopposite end of said cylinder, said discs being mounted normal to theaxis of said device and having sufficient diameter to intersect anyradiation having a direction which would avoid intersection with saidfirst shield.
 9. The device of claim 8 wherein said anode is connectedto an anode cap passing through one end of said cylindrical glassenvelope and said cathode is connected to leads which pass through theopposite end of said envelope and into a base comprising an insulatingmember having a series of parallel pins protruding therefrom; said basehaving a diameter slightly larger than said envelope and beingcontiguous with one end of said envelope; and said first shieldextending from said anode cap to said base and having an inner diameterapproximately equal to the diameter of said envelope to provide a snugfit thereon and an interference fit with said base.